import UIKit

var str = "Hello, playground"

// 显式定义浮点型常量

let PI:Float = 3.141592612312312

let PI2:Double = 3.14123456789123123123

// 隐式定义浮点型变量

var randomFloat = 12312.123323

var randomDouble = 2.3793758374597349879374

// 只要理解浮点型就是有小数点的就可以了..